Process for recovering iodine from iodine-containing aqueous glycol solutions



United States Patent PROCESS FOR RECOVERING IODINE FROMIODlNE-CONTAINING AQUEOUS GLYCOL SOLUTIONS Kfire'Ragnvald Fossan andGustav Allan Wetterholm,

Gyttorp, Sweden, assignors to Nitroglycerin Aktiebolaget, Gyttorp,Sweden, a corporation of Sweden No Drawing. Application September 8,1953, Serial No. 379,064

Claims priority, application Sweden September 15, 1952 4 Claims. (Cl.23-216) The present invention concerns the production of glycol bydirect oxidation of ethylene with oxygen in aqueous phase, when usingiodine as oxygen-transmitting agent, and more particularly, theinvention refers to a process for the recovery of iodine from thereaction mixture obtained in said oxidation process. This reactionmixture contains, besides glycols, free iodine, hydrogen iodide,iodohydrin, ethylene iodide and other oxidation products of ethylene,such as aldehydes and acids. It is of course a necessary condition, ifthe process is to be technically practicable at all, that the iodineshould be recovered in a simple way and practically quantitatively.

The present invention supplies a solution of this problem. The inventionis based upon the experimental investigations which have shown that itis possible to precipitate iodine from such reaction mixtures containingglycol and other substances by treating them with oxidizing agents undercertain conditions, without this having any injurious effect upon theother constituents of the mixture.

On the basis of these results the process according to the inventionconsists therein that the said reaction solution is treated with suchoxidizing agents as have a redox potential higher than thatcorresponding to the reaction 2l'=I2+2E, for which reaction E=0.54.

Examples of such oxidation agents are chlorine, nitrogen oxides,potassium permanganate, hydrogen peroxide, ferric chloride, hypochlorousacid, chromium trioxide etc. Substances from which the oxidation agentsare liberated under the infiuenceof acid are also usable, e. g. sodiumnitrite alone or with simultaneous addition of oxygen. The addition ofthe oxidizing agent to the reaction mixture may also take place withsimultaneous mechanical stirring of the mixture.

By the treatment according to the invention in the first place iodine isprecipitated from the hydrogen iodide, and at the same time the iodinethat is bound in complexcompounds is liberated. iodine that is presentin the solution in the form of iodohydrin or diiodide is notprecipitated directly, but by hydrolysis these compounds may easily beconverted to hydrogen iodide, from which the iodine is thenprecipitated. In this way it is possible to recover quantitatively thewhole amount of iodine employed in the oxidation of ethylene.

The manner of carrying out the process according to the invention isdescribed in greater detail below in the following non-limitativeexamples.

Example 1 The reaction mixture to be treated had the followingcomposition in respect of iodine compounds:

Percent Free iodine 0.69 Hydrogen iodide, reckoned as I2 3.13Iodohydrin, reckoned as T2. 0.31

or a total iodine-content of 41.7 g./ 1000 g. solution.

In this reaction a mixture of nitrose and oxygenwas introduced at roomtemperature, with simultaneous me- 2,780,528 Patented Fees, 1957chemical stirring. A wash bottle with nitrose was connected up with theoxygen supply conduit as a shunt, and by regulating that part of theoxygen that passed throughthe nitrose vessel it was possible to vary theratio of the gases. In this example the amount of nitrose in the gasintroduced was 15%. Iodine was precipitated in the crys talline formfrom the hydrogen iodide, and at the same time also the iodine occurringin the solution bound in complex form was precipitated. The introductionof gas was continued to the point at which all the hydrogen iodide hadbeen oxidized, which is easily established, as reddish brown clouds ofprecipitated iodine are no longer formed at the end of the tube throughwhich the gas is introduced, when the precipitation is complete, and thesolution is then completely clear. When introducing the gas care wastaken to avoid excess of nitrose:oxygen so that the solution should notbecome unnecessarily acid.

The precipitated iodine was easily separated by filtering with a Buchnerfunnel. Only iodine in the form of ethylene iodohydrin was then left inthe filtrate. In order to recover this, the solution was made alkalineand heated to 70 to C. for 2 to 3 hours, whereby the iodine compound wascompletely hydrolyzed. By cooling and acidifying free hydrogen iodidewas obtained, which was precipitated in the crystalline form by renewedtreatment with a mixture of nitrogen oxides and oxygen and filtered off.The amount of iodine recovered in this way was 41.1 g./1000 g. solution,i. c. 98.6% of the amount of iodine present.

Example 2 In this case the reaction solution had the followingcomposition in respect of iodine compounds:

Percent Free iodine 0.05 Hydrogen iodide, reckoned as I2 1.91lodohydrin, reckoned as is 1.85

Consequently, the total amount of iodine corresponded to 38.2 g./ 1000g. solution.

Through this reaction mixture a stream of chlorine gas was conducted atroom temperature and with me chanical stirring. In the same way as inthe foregoing example iodine was precipitated from the hydrogen iodideand from dissolved compounds containing iodine bound in complex form,and filtered off. The iodohydrin was then hydrolyzed and the treatmentfurther carried out in the same way as in Example 1, but using chlorinefor the precipitation of the iodine in the second step and avoidingexcess of chlorine. The amount of iodine recovered in this way was 38,8g./ 1000 g. solution, i. e. 101.5% of the amount of iodine originallyemployed, which within the limits of error for the analytic resultsindicates that a quantitative recovery was attained.

Example 3 The reaction solution to be treated had the followingcomposition in respect of iodine compounds:

Percent Free iodine 0.07 Hydrogen iodide, reckoned as I2 3.45Iodohydrin, reckoned as I: 0.10

Consequently, the total amount of iodine compounds in the solution was3.62%.

To 300 g. of this solution was added H2804 (50%) in an amount equivalentto the amount of hydrogen iodide in the solution. Then NaNOz was addedsuccessively, while continuously stirring. The addition took placeduring 15 minutes and a total amount of 2 g. sodium nitrite was added,whereby the iodine was precipitated in the crystalline form. Afterfiltering off the iodine, NaOH (10%) was added to the solution in anamount suflicient to create alkaline reaction and the solution washeated on water bath for 2 hours. During this time the reaction of thesolution was controlled and more sodium hydroxide was added, whenrequired, to maintain the alkaline reaction. By this treatment theiodohydrin was hydrolyzed. After acidifying with diluted H2504, theiodine liberated by the hydrolysis was precipitated by adding 0.1 g.NaNOz. The amount of iodine recovered was 10.7 g. or 98.7% of the totalamount of iodine compounds originally present in the solution.

Example 4 The composition of the reaction solution to be treated inrespect of iodine compounds was as follows:

Percent Free iodine 0.68 Hydrogen iodide, reckoned as I2 2.45lodohydrin, reckoned as Is 0.70

or a total iodine content of 38.3 g./ 1000 g. solution.

To 200 g. of this solution was added 50 g. hydrogen peroxide (3%). Themixture was left to stand for 1 /2 hours at room temperature, wherebythe iodine was precipitated in the crystalline form. The iodohydrin wasstill unaltered in the solution and the iodine from this compound wasrecovered in the following manner: after filtering ed the iodine alreadyprecipitated, NaOI-I was added to the solution in an amount sufiicientto make the solution alkaline and the solution was then heated on waterbath for 2 hours. from time to time and more sodium hydroxide was addedwhen required for maintaining the alkaline reaction. The solution wasthen acidified with diluted sulphuric acid, whereupon ml. hydrogenperoxide (3%) was added. The solution was then left to stand for 1 hour,whereby the iodine previously contained in the iodohydrin wasprecipitated and then filtered 0E. The recovered amount of iodine was7.55 g. which corresponds to 98.5% of the amount of iodine originallypresent in the solution.

Example 5 In this :case a reaction solution of the same composition asin Example 3 was treated. Consequently, it contained 0.07% free iodine,3.45% hydrogen iodide, reckoned as I2, and 0.10% iodohydrin, reckoned as12, e. g. a total iodine-content, reckoned as 12, of 3.62%.

To 300 g. of this solution sodium hypochlorite solution of aconcentration corresponding to 74.3 g. active chlorine per litre wasadded while shaking. After addition of ml. hypochlorite solution, thetotal amount of iodine present as hydrogen iodide was precipitated inthe crystalline form. The solution was then made alkaline by addingsodium hydroxide (10%) and thereupon heated on water bath 2 hours,whereby the iodohydrin was hydrolyzed. After cooling, diluted sulphuricacid was added in an amount equivalent to the amount of sodium hydroxidepreviously added. and the remaining iodine was precipitated by adding 1ml. sodium hypochlorite solution. The recovery of iodine wasquantitative.

What we claim is:

1. In the recovery of iodine from aqueous glycol solutions containingdissolved free iodine, hydrogen iodide and hydrolyzable organic iodinecompounds; the process which comprises treating such a glycol solutionwith a suflicient amount of an oxidizing agent, selected from the classconsisting of chlorine, nitrogen oxides, potassium permanganate,hydrogen peroxide, ferric chloride, hypochlorous acid, chromium trioxideand substances capable of generating these oxidizing agents The reactionof the solution was controlled in the solution, to .:OXldl.Z the iodidespresent without alfecting the glycol and the hydrolyzable iodinecompounds, thereby precipitating free iodine, hydrolyzing the saidhydrolyzable iodine compounds by making the solution alkaline andheating to water bath temperatures, acidifying the solution and againtreating the solution with a sufficient quantity of said oxidizing agentto precipitate iodine from the products resulting from the hydrolysis,and recovering the precipitated iodine.

2. In the recovery of iodine from aqueous glycol solu- Zions containingdissolved free iodine, hydrogen iodide and hydrolyzable organic iodinecompounds; the process which comprises treating such a glycol solutionwith an oxidizing agent, selected from the class consisting of chlorine,nitrogen oxides, potassium permanganate, hydrogen peroxide, ferricchloride, hypochlorous acid, chromium trioxide and substances capable ofgenerating these oxidizing agents in the solution, the concentration ofsaid oxidizing agent being suflicient to oxidize the iodides present andthereby to precipitate free iodine without aflEecting the glycol and thehydrolyzable organic iodine compounds, filtering off the precipitatediodine, making the remaining solution alkaline and heating it tohydrolyze the hydrolyzable iodine compounds, acidifying the solution andagain treating it with said oxidizing agent to precipitate the remainingiodine from the solution, and filtering off the precipitated iodine.

3. In the recovery of iodine from aqueous glycol solutions containingdissolved free iodine, hydrogen iodide and hydrolyzable organic iodinecompounds; the process which comprises treating such a glycol solutionwith an oxidizing agent having a redox potential higher than thatcorresponding to the reaction l=I2+2E, the constant E for said reactionbeing 0.54, and being capable of oxidizing the iodides present withoutaffecting the glycol and hydrolyzable iodine compounds, separating theiodine thus precipitated, making the remaining solution alkaline,heating to water bath temperatures to hydrolyze the remaining iodinecompounds, again treating with said oxidizing agent to precipitateiodine from the products of hydrolysis and again separating theprecipitated iodine.

4. In the recovery of iodine from aqueous glycol solutions containingdissolved free iodine, hydrogen iodide and hydrolyzable organic iodinecompounds; the process which comprises treating such a glycol solutionwith a mixture of nitrose and oxygen, separating the iodine thusprecipitated, making the remaining solution alkaline, heating to waterbath temperatures to hydrolyze the remaining iodine compounds,thereafter treating with a mixture of nitrogen oxides and oxygen toprecipitate iodine from the production of hydrolysis and againseparating the precipitated iodine.

References Cited in the file of this patent UNITED STATES PATENTS1,708,287 Turrentine Apr. 9, 1929 1,936,553 Jones Nov. 21, 19332,385,483 Wolfi Sept. 25, 1945 FOREIGN PATENTS 55,232 Norway May 27,1935 OTHER REFERENCES Middel: Chemical Abstracts, vol. 37, 1943, column59. Handbook of Chemistry and Physics, Chemical Rubber Publishing Co.,30th edition, 1947, pp. 1418 to 1420.

1. IN THE RECOVERY OF IODINE FROM AQUEOUS GLYCOL SOLUTIONS CONTAININGDISSOLVED FREE IODINE, HYDROGEN IODIDE AND HYDROLYZABLE ORGANIC IODINECOMPOUNDS; THE PROCESS WHICH COMPRISES TREATING SUCH A GLYCOL SOLUTIONWITH A SUFFICIENT AMOUNT OF AN OXIDIZING AGENT, SELECTED FROM THE CLASSCONSISTING OF CHLORINE, NITROGEN OXIDES, POTASSIUM PERMANGANATE,HYDROGEN PEROXIDE, FERRIC CHLORIDE, HYPOCHLOROUS ACID, CHROMIUM TRIOXIDEAND SUBSTANCES CAPABLE OF GENERATING THESE OXIDIZING AGENTS IN THESOLUTION, TO OXIDIZE THE IODIDES PRESENT WITHOUT AFFECTING THE GLYCOLAND THE HYDROLYZABLE IODINE COMPOUNDS, THEREBY PRECIPITATING FREEIODINE, HYDROLYZING THE SAID HYDROLYZABLE IODINE COMPOUNDS BY MAKING THESOLUTION ALKALINE AND HEATING TO WATER BATH TEMPERATURES ACIDIFYING THESOLUTION AND AGAIN TREATING THE SOLUTION WITH A SUFFICIENT QUANTITY OFSAID OXIDIZING AGENT TO PRECIPITATE IODINE FROM THE PRODUCTS RESULTINGFROM THE HYDROLYSIS, AND RECOVERING THE PRECIPITATED IODINE.